The present invention relates generally to an information recording medium having an area which is optically readably printed in a given format with a code image comprising an arrangement of a plurality of dots corresponding to data containing at least information such as sound, video and text. More particularly, the present invention relates to a system for checking the quality of such a code image.
For example, in published European applications EP 670,555 and 717,398 assigned to the same assignee as this application are disclosed a dot code which is a code image for allowing data containing information, such as sound, video, or text, to be optically readably printed at high density in a given format and a code image reading device for optically reading the dot code by an operator""s manual scanning operation and reproducing information such as original sound.
Here, FIG. 8 shows a physical format of such a dot code.
As shown in FIG. 8, a dot code 100, representing information, such as sound, in the form of an arrangement of dots, is two-dimensionally divided into a plurality of blocks 101. Each block is composed of a data area 103, markers 102, a pattern dot area 104, and a block address pattern area 105.
In the data area 103 of each block there exists data as a dot image of white or black dots indicative of 0s or 1s arranged in a predetermined format. The markers 102 are used to find a reference point for detecting each dot in the data area and are located at four corners of each block. These markers, defining the blocks, are arranged at regular intervals from top and bottom and from left to right. In each block, its associated pattern dot area 104 is located between the left-side markers 102 and its associated block address pattern area 105 is located between the bottom markers and has an error detecting or correcting code. The block address pattern area is used to identify the corresponding block in a read operation.
FIG. 9 shows a block diagram of the conventional code image reader for optically reading the dot code 100.
As shown in FIG. 9, the code image reader comprises an imaging unit 201, an image memory 202, a binarization unit 203, an image memory 204, a restoration unit 205, and a reproduction unit 206. In more detail, the restoration unit 205 comprises a center-pixel-in-dot detecting section 205a and a dot decision section 205b, and the reproduction unit 206 comprises a demodulation section 206a, an interleave memory 206b, an interleave and error correction section 206c, and an output section 206d. 
The imaging unit 201 is equipped with an illumination section having a light emitting diode (LED) for illuminating the dot code 100, a solid state imaging device such as a charge coupled device (CCD), and an optical system for focusing reflected light from the dot code onto the CCD. The image memory 202 subjects an image signal output from the imaging unit to digitization and then stores the resulting digital image signal. The binarization unit 203 subjects the digital image signal read from the image memory 202 to thresholding for binarization. The image memory 204 stores the resulting two-valued image data from the binarization unit 203. The restoration unit 205 detects dots from the two-valued image data read from the memory and allocates a value of either 0 or 1 for each dot to thereby output dot arrangement data. The reproduction unit 206 is responsive to the dot arrangement data from the restoration unit to reproduce the original information such as sound.
The code image reader thus arranged, even if the size of the entire dot code is larger than the field of view, or the imaging area 100a, 100b of the imaging unit 201, allows the dot code to be read by scanning each of consecutive image regions in sequence by manually moving the imaging unit 201 over the code image in the direction indicated by an arrow.
That is, even if the entire dot code 100 cannot be imaged at one time, the original data can be reconstructed from dot arrangement data in each block 101 if the address assigned to each block can be read and recognized correctly.
Thus, the code image techniques described above allow a lot of information to be stored at high densities on media such as paper, which is impossible with conventional one-dimensional or two-dimensional bar codes. The techniques, which allow easy transfer of information, such as sound, through paper, have been increasingly expected to find extensive applications which have not been supposed so far.
Here, the binarization unit 203 is arranged to control adaptively the threshold value for binarization according to printing conditions of the code image, for example, the density of white dots (paper surface) or black dots. Even if the printing quality of the code image is somewhat bad, therefore, an appropriate operation is performed accordingly.
In reading the two-valued image data from the image memory 204 and detecting dots, the restoration unit 205 is arranged to control adaptively the reference points for detecting the dots according to printing conditions of the code image, i.e., printing displacements of the dots and their deformation. As in the binarization unit 203, even if the printing quality of the code image is somewhat bad, the restoration unit performs an appropriate operation accordingly. The restoration unit, which is basically constructed from the central-pixel-in-dot detecting section 205a and the dot decision section 205b, first detects the markers 102 and then, on the basis of the pattern dot reading reference point determined by the detected markers and format information, searches the pattern dot area 104 for each dot and computes the dot detecting reference point for which an error function defined by distances between the ideal centers of dots constituting the pattern dot area 104 and the centers of the corresponding dots actually searched for is minimized.
This search operation is described in Japanese Unexamined Patent Publication No. 8-171620.
The restoration unit further detects the central pixel in each dot on the basis of the detecting reference point thus computed, decides whether the detected dot is black or white, allocates a value of either 1 or 0 for the detected dot, and outputs dot arrangement data. Thus, even if the printing quality of the code image having dots printed at high density is bad, the code image can be read quite satisfactorily.
Such code images will be printed under various printing conditions including various types of printing machines, various printing materials such as paper and inks, and printing machine management methods. Thus, in order to allow code images to be read stably at all times, it is required to maintain always the printing quality of code images themselves constant.
In general, the quality control of conventional bar codes is performed on the basis of the width and the density or contrast of bars specified in JIS standards JIS X 0501, 0502 and so on.
Specifically, the quality is checked using a checking device as disclosed in, for example, Japanese Unexamined Patent Publication No. 5-77530.
As described above, however, in a code image reader for optically reading a code image having dots printed at high density, such as dot code 100, even if the printing quality of the code image is not good, the binarization unit 203 and the restoration unit 205 operate adaptively to read the code image successfully. Thus, the utilization of the bar code checking method for code images without modification results in an increase in the checking time and the size of the checking device. In addition, the checking method is no longer suitable for checking devices for checking high-density code images. Therefore, there arises need to establish anew a quality checking method that is the most suitable for high-density code images.
From a standpoint that the original purpose of checking the quality of a code image itself is to confirm whether original information such as sound can be recovered with certainty from that code image, it can be said that the most suitable checking method is to read the code image to be checked with the code image reader and then confirm whether the original information can be reproduced or not.
However, this approach still has the checking time problem. In addition, in view of the uncertainty of reading by manual scanning, the confirmation alone makes it difficult to allow the inspection to have correctness or objectivity. It is thus impossible to say that the method is perfect. For example, if the original data is sound information, it takes long to reproduce sound. The inspection based on the sense of hearing results in lack of correctness or objectivity.
The manual scanning is subject to variation from time to time. In the case of abnormal manual scanning, even if the quality of the code image is good, the original information may not be reproduced. Further, even if the original information is reproduced with optimum manual scanning, the next manual scanning may fail to reproduce the original information.
It is therefore an object of the present invention to provide a code image quality checking device and method which minimizes the time required to check the quality of code images and is suitable for code images having dots printed at high densities.
To attain the object, there is provided a code image quality checker for checking the quality of a code image which contains a plurality of dots arranged in accordance with data containing at least sound information and is optically readably recorded in a given format on a portion of a recording medium, comprising: imaging means for capturing the code image on the recording medium and outputting an image signal; binarization means for subjecting the image signal from the imaging means to binarization to output two-valued image data; restoration means for detecting the dots from the two-valued image data and allocating each of the dots detected for a value of either 1 or 0 to output dot arrangement data; reproduction unit responsive to the dot arrangement data from the restoration means to recover the data containing at least sound information; adaptive read control means for adaptively controlling the operation of each of the imaging means, the binarization means, the restoration means, and the reproduction means according to the quality of the code image; and parameter information output means for outputting to outside parameter information used by the adaptive read control means to control adaptively the operation of each of the imaging means, the binarization means, the restoration means, and the reproduction means, the parameter information being employed to check the quality of the code image.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.